1. Technical Field of the Invention
The present invention relates generally to tire location detecting apparatuses for automatically detecting the locations of tires on a vehicle and tire inflation pressure detecting apparatuses for detecting the inflation pressures of tires on a vehicle.
More particularly, the invention relates to an efficient tire location detecting apparatus which is integrated into a direct-type tire inflation pressure detecting apparatus.
2. Description of the Related Art
Conventional direct-type tire inflation pressure detecting apparatuses generally include a plurality of transmitters and a receiver.
Each of the transmitters is directly installed to one of a plurality of wheels of a vehicle and includes a pressure sensor working to sense the inflation pressure of a tire mounted on the wheel. Each of the transmitters is configured to transmit a pressure signal representative of the inflation pressure of the tire sensed by the pressure sensor.
The receiver is installed to the body of the vehicle and includes at least one antenna. The receiver is configured to receive the pressure signals transmitted from the transmitters through the antenna and determine the inflation pressures of the tires based on the respective received pressure signals.
In the above arrangement, in addition to the pressure signals sent out from the transmitters, the receiver may also receive pressure signals that are sent out from external transmitters. However, it is impossible for the receiver to determine whether a pressure signal received thereby has been sent out from one of the transmitters or from an external transmitter. Moreover, it is also impossible for the receiver to detect the locations of the transmitters (i.e., the tires) on the vehicle. In other words, the receiver cannot determine the wheel to which the transmitter having sent out a pressure signal and the tire whose inflation pressure is indicated by the pressure signal are mounted.
To solve the above problems, each of the transmitters may be configured to transmit an identification signal (to be referred to as ID signal hereinafter) representative of the identity thereof along with the pressure signal. On the other hand, the receiver may be configured to have registered therein reference ID signals, each of which coincides with the ID signal of one of the transmitters and is associated with the location of that transmitter.
Thus, the receiver may work to compare an ID signal received thereby with the reference ID signals registered therein and identify the transmitter which has sent out the ID signal when the ID signal coincides with one of the reference ID signals.
Consequently, the receiver can identify the wheel to which the identified transmitter is mounted. More specifically, the receiver can determine whether the wheel is a FR (front-right), a FL (front-left), a RR (rear-right), or a RL (rear-left) wheel of the vehicle. Further, the receiver can determine the inflation pressure of the tire fitted on the identified wheel based on the pressure signal received along with the ID signal.
However, with the above configuration, it is required to previously register the ID signals specific to the respective transmitters as reference ID signals in the receiver through associating the ID signals with the locations of the respective transmitters on the vehicle (i.e., the wheels on which the respective transmitters are mounted). Moreover, as tire replacement or rotations are performed, it is required to update the reference ID signals in the receiver.
However, the registration of the ID signals in the receiver is a time-consuming task, and thus it is required to automatically perform the registration task. Further, for automatically performing the registration task, it is required to automatically detect the locations of the transmitters (i.e., the locations of the associated tires) on the vehicle.
To meet the above requirements, U.S. Pat. No. 5,602,524 proposes a method, according to which a triggering device is provided for each of the wheels to transmit a trigger signal, one of the transmitters transmits the ID signal specific thereto to the receiver upon being triggered by the trigger signal, and the receiver associates the ID signal and the location of the triggered transmitter and registers therein the ID signal as a reference ID signal.
However, with this method, a triggering device is required for each wheel, thus increasing the parts count and manufacturing cost of the tire inflation pressure detecting apparatus.
International publication No. WO 031089260 proposes a method, according to which a dual axis accelerometer is provided in each transmitter to automatically detect the location of the transmitter and thus that of the tire associated with the transmitter.
However, with this method, it is only possible to determine the right/left location of the transmitter.
U.S. Pat. No. 6,018,993 proposes a method, according to which the receiver accumulates the strengths of signals received from the transmitters via respective receiving antennas and determines the locations of the transmitters based on the respective accumulated strengths of signals.
However, with this method, it takes time to accumulate the strengths of signals. Moreover, an additional means (or device) is required to perform the accumulation task, increasing the manufacturing cost of the tire inflation pressure detecting apparatus.
U.S. Pat. No. 6,489,888 proposes a method, according to which the receiver determines the locations of the transmitters based on the respective distributions of RSSI (Received Signal Strength Indicator) values for signals transmitted from the transmitters.
However, with this method, it takes time to obtain the distributions of RSSI values. Moreover, an additional means (or device) is required to obtain the distributions of RSSI values, increasing the manufacturing cost of the tire inflation pressure detecting apparatus.